In certain known types of overhead cam engines, the lobes of the camshaft directly contact the respective valves to actuate the valves. In other known types of overhead cam engines, the lobes of the cam do not directly contact the valves for valve actuation. Rather, a cam follower is positioned between the cam lobe and the valve stem and the cam lobe actuates the cam follower which, in turn, actuates the valve.
In a specific type of such an engine, such as a General Motors Northstar®, High Value V6® or Ecotech® engine, as shown in FIG. 1 (Prior Art), the cam follower 10 has a longitudinal beam 12 having a first end 14 and a second end 16. The first end 14 rests on a static hydraulic lash adjuster 18 via seat 68 on the beam 12 and the second end 16 bears on the valve stem 20 to actuate the valve 22. A cam roller 24 having an axis of rotation 26 perpendicular to a longitudinal plane of the follower beam 12 is rotationally mounted on the beam 12 between the first end 14 and the second end 16 to contact and provide a low friction engagement with the cam lobe 28 of camshaft 30. Thus, the cam lobe 28 rotates against the follower cam roller 24, thereby moving the cam roller 24 and cam follower 10 in a direction of actuation. Since the first end 14 of the follower beam 12 rests on the static hydraulic lash adjuster 18 via seat 68, the movement of the cam lobe 28 and cam roller 24 is transmitted to the valve stem 20. The second end 16 of the follower beam 12 includes generally a polished curved surface 36 (see FIG. 8) that engages the valve stem 20 to actuate the valve 22. This is a relatively high friction engagement, especially with the forces resulting from actuating the valve 22 against the force of the valve spring 34. Fingers 70 (see FIGS. 1, 7 and 8) maintain alignment of the follower 10 with the valve stem 20.
It is known to also provide valve stem rollers on overhead valve engine rocker arms to provide a low friction engagement between the rocker arm and the valve stem. However, in the typical roller cam follower 10 discussed above, which is generally significantly smaller than a counterpart rocker arm, the geometry and dimensions of the roller cam follower 10 prevent use of a valve stem roller at the second end 16 of the follower beam 12 for engaging the valve stem 20 because the follower beam 12 has insufficient length to correctly position a valve stem roller of a proper diameter over the valve stem 20 while avoiding interference between the valve stem roller and the cam roller 24.
It is therefore an object of the present invention to provide a roller cam follower that includes both a cam roller and a valve stem roller.
It is a further object of the present invention to provide a roller cam follower that reduces friction in the valve train as compared to conventional roller cam followers.
It is a further object of the present invention to provide a roller cam follower that includes both a cam roller and a valve stem roller within the same length as allowed by a conventional follower beam.
Other objects of the present invention will be apparent from the description below.